diff --git a/cookbooks/aws-parallelcluster-environment/libraries/directory_service_utils.rb b/cookbooks/aws-parallelcluster-environment/libraries/directory_service_utils.rb
index c24e30757c..d8f823446d 100644
--- a/cookbooks/aws-parallelcluster-environment/libraries/directory_service_utils.rb
+++ b/cookbooks/aws-parallelcluster-environment/libraries/directory_service_utils.rb
@@ -21,7 +21,7 @@ def parse_arn(arn_string)
 def _get_cn_subparam(param)
   tokens = param.split(",") unless param.blank?
   tokens.each do |token|
-    return token if token.include? "cn"
+    return token if token.downcase.start_with? "cn"
   end
   ""
 end